Conventional assembly line manufacture of seamed articles constructed of limp fabric consists of a series of manually controlled assembly operations. Generally tactile presentation and control of the fabric-to-be-joined is made to the joining, or sewing, head under manual control. One drawback of this application technique is that the technique is labor intensive; that is, a large portion of the cost for manufacture is spent on labor. To reduce cost, automated or computer-controlled manufacturing techniques have been proposed in the prior art.
In the course of implementing such automated techniques, it is often necessary to locate and then precisely align a "corner" of an angularly oriented limp material workpiece with a reference position on a work surface. For the purposes herein, the term "corner" refers to a portion of a workpiece bounded by a generally convex peripheral edge, although that edge may include minor non-convex portions. The peripheral edge may be continuous or piecewise continuous (e.g. as may be formed by two straight edges extending to a common point).
In the prior art, angularly oriented segments have been slidingly translated in one or two directions on a work surface by an array of parallel endless belts driven by electric motor assemblies, for example as shown in U.S. Pat. No. 4,632,046. However, precise control and alignment of corners of limp material segments has not been accomplished. Moreover, prior art position control systems for controlling the position of a workpiece typically utilize stepper motor arrangements and/or DC motors in a servo loop arrangement. These systems utilize a controller, a driver, a feedback sensor, and a motor. In addition, appropriate electronics are required to integrate the elements into an operable system. These systems tend to employ extremely complex electrical and mechanical designs having inherent disadvantages, for example, heat dissipation constraints of the motors. Furthermore, these systems tend to be expensive and consume large quantities of electrical power during operation.
As an alternative approach in the prior art, pneumatic systems may be employed to position various objects. Conventional pneumatic positioning systems typically utilize a control unit, a pressurized pneumatic source, and a plurality of solenoid air valves coupled with a brake mechanism to axially control the relative position an air cylinder with respect to an associated rod. The solenoid valves generally are comprised of a direction valve for establishing the direction of the air cylinder travel, and may also include one or more velocity valves for establishing desired velocities of air cylinder travel. The control unit controls the solenoid air valves to move the air cylinder to a desired location with respect to the rod. Once the air cylinder has attained the desired spatial location relative to the rod, the control unit activates the brake mechanism, for example an air brake, to maintain the position of the air cylinder relative to the rod.
A primary shortcoming of the conventional pneumatic positioning systems is the limited response time of the air cylinder. In particular, these systems tend to respond slowly to commands from the control unit after the brake mechanism is activated. This shortcoming is due primarily to the limited and slow response of the brake mechanism, for example an air brake. After activation of the brake, it must be deactivated, which generally requires depressurization. Once the air brake is deactivated the system can then be directed to a new position.
There exists a need for low cost position control systems for finding and then controlling the position of corners of an oriented limp material segment.